Grafana expects a response containing an array of annotation objects in the
following format:

[
{
annotation: annotation, // The original annotation sent from Grafana.
time: time, // Time since UNIX Epoch in milliseconds. (required)
title: title, // The title for the annotation tooltip. (required)
tags: tags, // Tags for the annotation. (optional)
text: text // Text for the annotation. (optional)
}
]

Note: If the datasource is configured to connect directly to the backend, you
also need to implement an OPTIONS endpoint at /annotations that responds
with the correct CORS headers: